This invention relates to a fingerprint processing system for use in processing a fingerprint image to detect a position of a core in the fingerprint image and/or to detect directions and curvatures of ridges of the fingerprint image prior to detection of the position of the core.
It is a recent trend that a fingerprint is processed to be automatically identified by a pattern recognition technique in an electronic computer. Automatical identification of the fingerprint is made with reference to abrupt endings, bifurcations, and branches which are extracted from a fingerprint image and which may be collectively called minutiae. In order to accurately identify or collate the fingerprint, it is necessary to detect directions of ridges of the fingerprint and to decide a position of a core in the fingerprint, prior to identification of a fingerprint by the use of such minutiae. Detection of the directions and decision of the position of the core will be collectively referred to as preliminary processing hereinafter.
Heretofore, preliminary processing is carried out by processing a sequence of picture elements of a fingerprint image which is two-dimensionally quantized and which appears as a black-and-white image. The picture elements are arranged on a predetermined coordinate system, for example, an orthogonal coordinate system. More specifically, proposal has been proposed in Japanese Patent Publication No. Syo 52-97298, namely, 97298/1977, about detecting directions of ridges by the use of the fact that a black-and-white level or a density level of picture elements in the black-and-white image is scarcely varied when each ridge is traced along the same direction as each direction of the ridges while the density level is largely varied when each ridge is traced along a direction orthogonal to each direction of the ridges. For this purpose, the fingerprint image is traced on the straight from each picture element to calculate a variation of the density level. Such straight tracing of the fingerprint image, however, makes it difficult to calculate a curvature of each ridge in principle. In addition, a large variation of the density level takes place on the straight tracing also at an area, such as a core of the fingerprint, a triangle portion, because a curvature is very large in the area.
In order to determine a core in a fingerprint image having a plurality of ridges laid from an upper portion of the fingerprint image to a lower portion, the ridges have been successively traced in Japanese Patent Publication No. Syo 58-55549, namely 55549/1983, from the upper portion towards the lower portion to detect a summit or top portion of each ridge and to decide a top position of an innermost one of the ridges as the core of the fingerprint image.
Herein, it is to be noted that there are various types of fingerprints, such as arches, loops, whorls, and the like, and that no innermost ridge is present in a fingerprint of an arch type. Accordingly, it is difficult to determine a position of the core in the fingerprint of the arch type.
Moreover, it frequently happens that fingerprint images have a low quality of images and are unclear at center portions of the fingerprint images. In this event, it is difficult with the above-mentioned method to determine cores in such fingerprints of low quality without any help of an operator. Therefore, it takes a long time to adjust and confirm each position of the cores by the operator.